The present invention relates to a continuity angle controlled self-excited inverter circuit for use in a high-frequency switching power source requiring a high reliability.
Concerning the switching power source to control a self-excited inverter circuit and its output with a magnetic amplifier, one like that shown in FIG. 10 is commonly known. Such a switching power source circuit comprises a self-excited inverter circuit consisting of a main transformer 1, alternate, switching elements 5 and 6 and a saturation reactor unnumbered and a DC circuit 3, which are connected to the primary winding 2 of the main transformer 1, and magnetic amplifiers 9 and 10, a commutator 11, a smoothing filter circuit 12 and a error detection amplifier circuit 13 which are connected to the secondary winding 8 of the main transformer.
Said circuit has been used widely because of its simple construction and highly reliable components. In this circuit, when the product of V.sub.2 .times.T=2 (V.sub.2 : Voltage of secondary winding 8, T: Period) is maintained for a certain period of time, the saturation reactor saturates, and the current commutates from the first FET 5 to the second FET 6 as known already. The secondary voltage V.sub.2 of the main transformer 1 is controlled by the magnetic amplifiers 9 and 10 to obtain a constant output voltage V.sub.o.
The conventional circuit as is described in the foregoing is disadvantageous in that, as far as the relationship of the input voltage Vi and output voltage Vo shown in FIG. 11 is concerned, the uncontrolled secondary output voltage V.sub.2 is in direct proportion to the input voltage Vi as indicated by the dotted line representing its characteristic. On the other hand, however, when the output voltage Vo is controlled by the magnetic amplifiers 9 and 10, said output voltage Vo has the characteristic represented by a solid line shown in FIG. 11 and becomes constant from a certain point on. The product Vma (represented by slant lines) obtained by multiplying the difference of these characteristics V.sub.2 and V.sub.o by the voltage and time becomes a load on the operation of the magnetic amplifiers 9 and 10. FIGS. 12 and 13 respectively represent Vi(L), the case where the input voltage is low, and Vi(H), the case where the input voltage is high, corresponding to the cases shown in FIG. 11, wherein the areas covered with slant lines respectively represent the products of the voltage and time Vma(L) and Vma(H). As is clear from FIGS. 12 and 13, when the input voltage is Vi(H), the case of a high input voltage (see FIG. 13), Vma(H), the product the voltage and time, will increase to cause the loss by the heat, the fall of efficiency and the resulting inability to follow a wide range of variation of input voltage Vi.